A. Field of the Invention
The present invention relates to a cooling/guiding method and to a cooling/guiding apparatus that will be used when a film of a thermoplastic synthetic resin or the like is to be produced by the inflation method or the T-die method. More specifically, the invention relates to an art in which the film is continuously passed through a section constituted by one or more air-introducing members having air intake ports, the air surrounding the film is intaken by the air-introducing members so that suction imparted to the film is balanced, and the film is guided into a predetermined path so that the film is separated from the air-introducing members.
B. Description of the Prior Art
A molding method such as the inflation method or the T-die method is employed for the production of flat films and bags of thermoplastic synthetic resins (often containing a variety of fillers) such as polyethylene, polypropylene and the like.
First, the inflation method will be roughly described below with reference to FIG. 1. Pellets of a thermoplastic synthetic resin are thrown from a hopper 10 into an extrusion molding machine 12 where they are heated, melted and extruded, and are passed over to a circular die 14. The extruded resin is inflated with the compressed air to form a cylindrical film or bubble 16. The bubble 16 is guided so as not to come out of a predetermined path with the outside thereof being cooled by a cooling/guiding apparatus 18. Thereafter, the bubble 16 is squeezed by stabilizer plates 20 and nip rollers 22, and is finally taken up flat by a winding machine, which is not shown, to obtain a flat film or a bag.
According to a manifold die method which is a representative T-die method, a wide reservoir portion (manifold) is provided at a position where the resin enters into the die from the extruding machine in a direction at right angles thereto, and the resin which is flattened by the manifold is extruded through a linear thin die outlet (lip). The resin is then passed through the cooling/guiding apparatus to obtain a flat film in the same manner as that of the above-mentioned inflation method.
Thus, the cooling/guiding apparatus is required for the inflation method or the T-die method because of the reasons mentioned below. First, to increase the molding speed so as to increase the production efficiency; second, to increase the clarity and strength of the film so as to improve the quality. The third reason stems from the manufacturing standpoint that the film is guided into a predetermined path to take it up maintaining a constant size.
According to U.S. Pat. No. 4,453,907 which discloses a cooling/guiding apparatus invented by one of the inventors of the present invention, there is taught a technique in which an enveloping circle is formed by the combination of a number of conduits, cooling water is passed through the conduits to cool the film that passes in contact with the enveloping circle, and the film is guided into a predetermined path.
According to the above conventional technique in which the film is cooled and guided while in contact with the apparatus (conduits), the film is not uniformly cooled, and thickness of the film varies irregularly. Further, the film is often damaged since it moves at a considerable speed while in contact with the conduits. Moreover, since the film must be brought into contact with the conduits, it is not feasible to increase the speed of travel of the film or to increase the molding speed.